1. Background of the Invention
The surface mounted resonator, because of its small size and lightweight, is built into, for example, portable electronic devices as a reference source for frequency and time. As one of these surface mounted resonators, there is a stacked resonator with particularly small thickness, and for example, there is a stacked resonator in which both of a vibrating plate and a holding plate are made of crystal, and these are directly bonded (refer to Patent Document 1).
2. Prior Art
FIG. 5 is an explanatory diagram of one conventional example of a stacked resonator, wherein FIG. 5A is a sectional view on arrow A-A in the lengthwise direction of the stacked resonator shown in FIG. 5B, FIG. 5B is a plan view of a vibrating plate 1, and FIG. 5C is a plan view of an outside bottom face 2c of the stacked resonator.
The stacked resonator has a rectangular shape in plan view, for example, with the dimension being 2.0×1.2 mm or 2.0×1.6 mm, and includes the vibrating plate 1 and a first holding plate 2, and a second holding plate 3, which have the same external shape. These are made of crystal with the same cutting angle, and stacked by direct bonding by, for example, siloxane bonding (Si—O—Si). However, the vibrating plate 1 and the first holding plate 2, and the second holding plate 3 are directly bonded beforehand in a state of a crystal wafer (not shown), and then divided into individual stacked resonators.
In the vibrating plate 1, a bottom face of a tuning fork base 1c of a crystal piece 1a having a tuning fork shape is coupled with an outer peripheral frame 1b by a connecting bar 1d. Each surface (both principal surfaces and both side faces) of a pair of tuning fork arms 1e has excitation electrodes forming pairs (not shown), and for example, a lead out terminal (not shown) is extended from one principal surface of the tuning fork base 1c to both lengthwise ends of the tuning fork arms 1e of the crystal piece 1a via, the connecting bar 1d. 
The first holding plate 2 and the second holding plate 3 are both formed in a concave shape in cross-section, for example, by etching. The first holding plate 2 has mounting terminals 4a and 4b (for example, two terminals) having a rectangular shape in plan view, along a widthwise direction, on both ends of the outside bottom face (one principal surface) 2c, which is flat. Moreover, the first holding plate 2 is electrically connected to the lead out terminals extended to both ends of the vibrating plate 1, by a through electrode or the like (not shown) provided on the first holding plate 2.
As shown in FIG. 5C, the mounting terminals 4a and 4b each have a dimension L1 in the lengthwise direction of the first holding plate 2, which is 0.6 mm, with a dimension (exposed length) L2 in the lengthwise direction of the first holding plate 2 in a central area (exposed surface of a base material) formed between the mounted terminals 4a and 4b being 0.8 mm. Furthermore these stacked resonators are bonded, as shown in FIG. 5A, to a circuit terminal 6 on a set substrate 5 by a lead-free solder 7, and mounted on a surface 5a of the set substrate 5.